ratelimiter

Rate Limiter

It is a rate limiter which can be exposed over gRPC. It has one method:

• Allow which receives an id from a Merchant and returns true or false depending on the usage.

The usage per Merchant is kept in memory, and it requires access to the Merchant Service to learn the MaxQPS per Merchant.

Testing

The rate limiter uses Golang rate package and runs completely in memory.

If a Merchant Service is listening on localhost, port 50051, then the Rate Limiter can be initialized as follows:

$ go run main.go --merchant-ip="::1" --merchant-port=50051 --port=50052

In a different terminal, please use the grpcurl tool to verify that the endpoints are working as expected.

• Merchant with MaxQPS>0

$ grpcurl -plaintext -d '{"id": "e1211351-bb91-441f-9ea0-3b243189dec6"}' "0.0.0.0:50052" ratelimiter.RateLimiterService/Allow | jq .allow
true

• Merchant with MaxQPS=0

$ grpcurl -plaintext -d '{"id": "84a8cb14-0e7b-43f5-8ec7-0840147d3d47"}' "0.0.0.0:50052" ratelimiter.RateLimiterService/Allow | jq .allow
null

• Too many requests

Merchant 6c1285c2-f09e-4a9b-8a6c-4d94695c1a15 has MaxQPS=10:

$ seq 1 20 | xargs -P $(sysctl hw.logicalcpu | cut -d" " -f2) -I % grpcurl -plaintext -d '{"id": "6c1285c2-f09e-4a9b-8a6c-4d94695c1a15"}' "0.0.0.0:50052" ratelimiter.RateLimiterService/Allow | jq .allow
true
true
true
true
true
true
true
true
true
true
null
null
true
null
null
null
null
null
null
null

• Merchant Service offline - merchant in memory

$ grpcurl -plaintext -d '{"id": "e1211351-bb91-441f-9ea0-3b243189dec6"}' "0.0.0.0:50052" ratelimiter.RateLimiterService/Allow | jq .allow
true

• Merchant Service offline - merchant not in memory

$ grpcurl -plaintext -d '{"id": "54c5b126-9a3b-4ecc-9590-e8bc5e9bd069"}' "0.0.0.0:50052" ratelimiter.RateLimiterService/Allow | jq .allow
ERROR:
  Code: Unknown
  Message: error reading max qps: rpc error: code = Unavailable desc = connection error: desc = "transport: Error while dialing: dial tcp 0.0.0.0:50051: connect: connection refused"